OBD2 S14 acting crazy, help - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

rim_bender · 10-25-2006, 01:18 PM

Im trygin to help my freind fix his car. It's a 1996 S14 so its OBD2 and an automatic.

two issues:

One, when you start out from a stop and floor it, it feels like it has no power at all, or seems like it alwasys starts in 2nd gear, cause as soon as it gets up in the rpms it starts to pull like it should.

Second, the idle is crazy, it idles up and down constantly between 300-600 rpms and almost shuts off sometimes.

The car thew three codes, knock sensor, vehicle speed sensor, and intake air temp sensor

The gear on teh speed sensor is chewed up so it wasnt even turning, so the speedo is not working. Could this be why the tranny starts in 2nd maybe?

the intake air temp sensor was swapepd with a kown good one.

All the codes were reset and the CEL has not come back on, but the car sill idles super bad and it still feels like it has no power down low or it starts in 2nd gear.

What could be wrong making the car do those two things?
__________________

Pank · 10-25-2006, 01:38 PM

havent addressed the knock sensor?

rim_bender · 10-25-2006, 03:03 PM

Quote:

Originally Posted by Pank

havent addressed the knock sensor?

the code never came back after we reset it, and the knock sensor has nothing to do with whats going on with the cars idle and werid power loss/or 2nd gear starts.

ia int worried about the knock sensor, just the other two problems

projectRDM · 10-25-2006, 11:19 PM

There's your problem. VSS and IAT would have no effect on idle or driveability, the VSS does nothing but send a speed signal, it can unplugged, removed, set on fire, etc. and have no bearing.
Same for the IAT, diagnositics use only. You can dip it in ice, burn it, or crush it to powder, the car doesn't care.
Knock sensor though does matter, and when the ECU reads a knock signal it will pull timing all the way out and run open loop. That would be the hesitation problem.
The idle problem is more than likely a vacuum leak, as a defective IAA would raise the idle to 1800 or so, a defective IACV would not allow it to idle period.
If the car is indeed starting in 2nd gear, adjust the inhibitor switch on the transmission and/or check for A/T codes through the diagnostic procedure outlined in the FSM.

10-25-2006, 01:18 PM	#1
rim_bender Zilvia Junkie Join Date: Jan 2004 Location: Ga Posts: 441 Trader Rating: (0) Feedback Score: 0 reviews	OBD2 S14 acting crazy, help Im trygin to help my freind fix his car. It's a 1996 S14 so its OBD2 and an automatic. two issues: One, when you start out from a stop and floor it, it feels like it has no power at all, or seems like it alwasys starts in 2nd gear, cause as soon as it gets up in the rpms it starts to pull like it should. Second, the idle is crazy, it idles up and down constantly between 300-600 rpms and almost shuts off sometimes. The car thew three codes, knock sensor, vehicle speed sensor, and intake air temp sensor The gear on teh speed sensor is chewed up so it wasnt even turning, so the speedo is not working. Could this be why the tranny starts in 2nd maybe? the intake air temp sensor was swapepd with a kown good one. All the codes were reset and the CEL has not come back on, but the car sill idles super bad and it still feels like it has no power down low or it starts in 2nd gear. What could be wrong making the car do those two things? __________________

10-25-2006, 01:38 PM	#2
Pank Post Whore! Join Date: Oct 2004 Location: Charlotte, NC Age: 42 Posts: 3,627 Trader Rating: (0) Feedback Score: 0 reviews	havent addressed the knock sensor? __________________ high performance driveway photography zenki s14---v8 fc rx7 my crappy flickr page (drift cars whoo)

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10-25-2006, 11:19 PM	#4
projectRDM Post Whore! Join Date: Dec 2002 Location: Atlanta Age: 51 Posts: 13,812 Trader Rating: (12) Feedback Score: 12 reviews	There's your problem. VSS and IAT would have no effect on idle or driveability, the VSS does nothing but send a speed signal, it can unplugged, removed, set on fire, etc. and have no bearing. Same for the IAT, diagnositics use only. You can dip it in ice, burn it, or crush it to powder, the car doesn't care. Knock sensor though does matter, and when the ECU reads a knock signal it will pull timing all the way out and run open loop. That would be the hesitation problem. The idle problem is more than likely a vacuum leak, as a defective IAA would raise the idle to 1800 or so, a defective IACV would not allow it to idle period. If the car is indeed starting in 2nd gear, adjust the inhibitor switch on the transmission and/or check for A/T codes through the diagnostic procedure outlined in the FSM.